Martyn Powell was working at a site belonging to his employers Cemex UK Materials in Saxon Street, Bletchley, when the incident happened in June last year.
Aylesbury Crown Court heard that Mr Powell was part of a team cleaning the area around the metal skip track at the asphalt plant. The track had been lifted into the air by a hoist to allow cleaning underneath.
The hoist jammed in the raised position and, as Mr Powell attempted to free it using a manual ratchet to pull down on the hoist, the hook gave way and the track suddenly fell, hitting his legs.
He was in hospital for a week and unable to work for six months.
An investigation by the Health & Safety Executive found that the company had failed to adequately maintain the hoist and had not provided a safe system of work in the event of its failure.
Cemex UK Materials Ltd, based in Surrey, was fined £35,000 and ordered to pay £10,043 costs after pleading guilty at an earlier hearing to breaching Section 2(1) of the Health and Safety at Work etc Act 1974 at an earlier hearing.
After the hearing, HSE inspector Karl Howes, said: “All machinery must be maintained regularly to ensure it is safe to work with.
"It is not enough to rely on reactive maintenance and only fix things when they go wrong; companies should be looking for signs of wear and tear before any deterioration leads to an incident and possible injury. In addition there needs to be a system of work in place so that workers know how to deal safely with the tasks involved in their job.
“Martyn Powell suffered painful fractures to both legs, but his injuries could easily have been more serious or even fatal.
“HSE will not hesitate to prosecute when companies neglect their equipment and put workers and others at risk.”